This invention relates to a swivel arm for supporting an appliance designed for use on a desk and more particularly this invention relates to a swivel arm for supporting a microfilm reader, having a telescope-type cantilever capable of swiveling about a pillar that can be vertically fixed to the desk, with a carrying frame for accommodating the appliance being provided at the end of the telescope-type cantilever.
Swivel arms of this kind are known and commonly used for supporting a telephone set. In the majority of cases they are employed to be able to swivel one individual telephone set in such a manner that it moves within the respective working area of two persons sitting at two desks placed side by side. The cantilever is supported on the vertical pillar about which it can swivel approximately 20 cm above the desk top, rendering it impossible for the cantilever to hit against objects on the desk. In order to be able to also adjust the distance between the carrying frame and the vertical pillar, the cantilever consists of two telescoping tubular sections. Manually releasable brakes retain the swivel arm in its respective positions, so that it does not intentionally move out of position when the dial of the telephone is operated.
Most recently even higher demands are being made on the ergonometrically correct dimensioning and positioning of appliances to be used at the working areas of individual operators. This is particularly true of microfilm readers or computer display units. With such appliances it is not only of importance that they have an optimal distance and angle in relation to the operator's eyes, but it is of essence that the display unit remain free of reflection, which impairs reading from the display unit. Hence, in supporting such appliances one has to provide for more freedom of adjustment than with telephone swivel arms hitherto known. In this connection it has to be kept in mind that a vertical adjustment of the cantilever on the vertical pillar can, for instance, not be considered, since the possibility of the cantilever pushing away objects on the desk when swiveled at a height of less than 20 cm above the desk top must be considered.
It is a primary object of this invention to design a swivel arm of the kind mentioned at the beginning in such a manner that even the level of an appliance held by it can be optimally adjusted, eliminating the possibility of the swivel arm being obstructed by objects on the desk when swiveling over it.
This object is established according to the invention in that the carrying frame is fixed at the end of the cantilever and in that it is capable of moving in an approximately vertical direction in relation to the cantilever.
This design renders it possible to achieve an optimal vertical adjustment of the appliance held by the carrying frame without a change in the cantilever's level such as predetermined by its design. The cantilever does not, therefore, hit against objects on the desk when being swiveled. Furthermore, it does not obstruct the operator's view by being positioned too high, since it can always be below the operator's eye-level.
A preferred embodiment of the invention provides for the carrying frame being capable of being vertically lowered down to the desk top. This embodiment is of particular advantage with microfilm readers of the keyboard type, since the keyboard can in this case rest on the desk top, which ensures easy operation and support from below and eliminates springing of the cantilever when the keyboard is being used.
The vertical adjustment of the carrying frame can be achieved with special design simplicity when the end of the cantilever is provided with an approximately vertical board having two guide rails, with an approximately vertical portion of the carrying frame gripping over the guide rails with two upper rails. This embodiment furthermore offers the advantage of being very rigid, which counteracts any tendency of vibration.
The carrying frame with the appliance held on it remains in any given vertical position when a tension-compensating flat spring with its associated take-up reel is located in the board and, when the free end of the tension-compensating flat spring reaches through the board and is connected to the carrying frame.
The appliance to be held by the carrying frame is firmly supported and protected from shocks when the carrying frame is designed as a cage that embraces the appliance to be held at least partially on three sides.
Another preferred embodiment of the invention is that the bottom of the carrying frame is capable of tilting about a pin supported in the side walls of the cage and that it can be locked in any desired position. This embodiment allows an infinitely variable fine-adjustment of the angle of inclination of an appliance placed on the carrying frame.
A large angle of inclination can be obtained when the pin of the bottom is positioned in front of the vertical line of gravity of the bottom bearing the load of the appliance to be held and when provision is made of a tension-compensating spring at the back of the bottom.
Since the appliance to be held by the swivel arm of the invention can be of considerable weight, it is imperative that the pillar be as firmly connected as possible to the desk. Experience has shown that fixing such pillars at the protracting edge of a desk top as practiced to date is in many cases not firm enough to resist the moment of tilt brought about by the weight of the appliance. Sufficiently firm support, can, however, be achieved when the vertical pillar has a locating plate that is or can be firmly connected to it and that can be placed on the desk top from above, and when it furthermore has a clamping arm capable of moving on the pillar, with the pillar reaching under the desk body in mounted condition.
Fixing the clamping pillar at the desk can be effected with special ease when the clamping arm consists of two movable clamping plates, with one clamping plate having a fastening screw in a threaded through-hole near its end pointing away from the pillar, with said fastening screw being capable of being pressed against the other clamping plate.
The bending and torsional forces acting in the cantilever are taken up particularly well when the cross-section of the cantilever has the shape of a rectangle pointing downward with its narrow side. A swivel arm with a cantilever of this kind has an extremely low tendency of vibration which is of importance with automatically controlled microfilm readers, since in this case considerable accelerating forces are present as a result of the fast film holder movements.
It is expedient for the design when the cantilever consists of a rectangular hollow section and of a supporting plate of rectangular cross-section that can be extended from it.
It is furthermore advantageous when on both sides of the supporting plate two upper rails are provided respectively that grip over one extension rail each, the latter in turn being connected to upper rails provided at the interior walls of the rectangular hollow section. A telescope-type guide is established in this way which can be manufactured at a relatively low price and which has a very high degree of strength, without the dimensions of the cantilever becoming so large that an undesired obstruction of the operator's view occurs.
The inclination of the carrying frame can be preset in a plurality of discrete positions when an angle bracket provided with several holes in a row is employed to hinge the carrying frame to a pin provided at the end of the supporting plate from above and at a slightly forward inclination, so that the pin reaches through any desired hole in the angle bracket.
The swiveling movement of the carrying frame about its approximately vertical axis at the free end of the cantilever can be influenced in respect of the carrying frame's resistance to change of position when the portion of the pin reaching above the angle bracket is provided with a compression spring, the degree of resilience of said compression spring being adjustable by means of a nut screwed onto the pin.
The carrying frame can be moved into the respective position of operation with special ease when grip handles are at the front end and at the side walls of the carrying frame.
A further preferred embodiment of the invention provides for a brake release lever being arranged on the grip handles for purposes of re-establishing the movability of the swivel arm. The brakes are actuated by releasing the grip handles, and in so doing also the brake release levers are actuated, eliminating the movability of the swivel arm and rendering it impossible for it to move unintentionally when in resting position.
Since in the majority of cases the appliance to be held on the carrying frame requires a power supply, it is advantageous for an electric cord to run through the vertical pillar and the cantilever to the carrying frame. The electric cord, therefore, does not cause any inconvenience on the desk.